AstroComb

The Most Precise Calibration Systemfor Astronomical Spectrographs

RESEARCH OBJECTIVES■ Spectroscopy of the solar atmosphere■ Search for Earth-sized exoplanets■ Observation of variable stars and galaxies■ Cosmological redshift measurements■ Measurement of the cosmic expansion■ Search for variations of the universal
constants

A P P L I C AT I O N S■ High-resolution spectroscopy■ High-precision radial velocity
measurements■ Near-infrared spectroscopy
K E Y F E AT U R E S
Artist view of the AstroComb spectrum superimposed over the La Silla Observatory (ESO)■ Collaborative system integration withsubsequent turn-key operation

S P E C T R O G R A P H C A L I B R AT I O N W I T H T H E A S T R O C O M B
Accurate analysis of the light emitted or absorbed by celestial objects requires spectrographs, which must be precisely calibrated. AstroCombs provide a stable and known
set of evenly spaced sharp spectral lines that act as reference points, enabling precise
calibration of the spectrograph’s wavelength scale. The comb-like pattern spreads
across a wide wavelength range in the visible and near-infrared, and illuminates
individual pixels of the spectrograph. The resulting high resolution provided by theAstroComb in any part of the spectrum cannot be achieved with traditional ThoriumArgon (ThAr) calibration lamps.
Calibration by AstroCombs is stable and repeatable, and reduces systematic errors,
all of which is important for long-term observations and for comparing data taken at
different times or by different instruments. E.g., the detection of exoplanets requires a
precision of 5 cm/s over years, and the direct observation of the accelerated cosmic expansion requires 1 cm/s over decades. A high level of automation makes calibration byAstroCombs efficient and particulary benefits large-scale astronomical studies.

Echelle spectrum of a thorium-argon (ThAr) lamp (channel A) above the evenly-spaced modes of an AstroComb (channel B)
at HARPS, ESO

1■ Regular line spacing■ Radial velocity resolution <2.5 cm/s
■ Tunable line positions to illuminate eachCCD pixel■ Uniform output spectrum, adaptable tospectrograph sensitivity■ Reference frequency given by atomicclock■ High long-term stability, state-of-the-art
short-term stability

S Y S T E M S I N O P E R AT I O N■ LARS, VTT, Teneriffe, ES■ FOCES, Wendelstein Observatory, DE■ Xinglong National Astronomical Observatory,CN■ HARPS, La Silla Observatory, CL■ ESPRESSO, Paranal Observatory, CL■ EXPRES, Lowell Observatory, US■ VELOCE, Anglo-Australian Telescope, AU■ NEID, Kitt Peak Observatory, US■ SPIRou, CFHT, Hawaii, US■ KPF, Keck Observatory, Hawaii, US■ MAROON-X, Gemini Observatory, Hawaii, USAstroComb

The Most Precise Calibration Systemfor Astronomical Spectrographs
SYSTEM COMPONENTS

Oscillator with CEO stabilization above and filtering cavities below (left), AstroComb system control rack (center), and the spectral flattening unit (right)

The AstroComb is a complete solution for spectrograph calibration in the visible and near-infrared spectral range. The system contains an optical frequency comb, a filter unit to adjust the comb mode spacing to the resolution of the spectrograph, an amplifierand spectral broadening unit, spectral flattening units for unstructured spectral characteristics, and system operation electronics
with software for full automation and remote control. An atomic clock serves as a reference to transfer its accuracy and stability to
all frequency comb modes.

Example of an echelle spectrum measured at the HARPS spectrograph at the ESO 3.6-metre telescope at the La Silla Observatory in Chile. The outputs from two independent
laser frequency combs were coupled to the two channels of the high-resolution spectrograph. Image credit: ESO

A S T R O C O M B - F R O M P L A N N I N G T O R O U T I N E O P E R AT I O N
Due to its high flexibility of configuration, the AstroComb’s unrivaled performance is available for both newly-commissioned highresolution spectrographs and as an upgrade for calibration sources of existing spectrographs. A sophisticated design process,characterized by close collaboration between the user facility and Menlo Systems, precedes each system installation and is key tosuccessful system operation. The system features and specifications are tailored to address an observatory’s specific instrumentation and research interests, providing the spectral range, comb mode spacing, and optical power required. A requisite service contract ensures continuous support by Menlo Systems’ experts, including on-site visits. With maturing user experience the AstroCombsystem operation becomes truly turn-key.
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AstroComb

The Most Precise Calibration Systemfor Astronomical Spectrographs
MENLO SYSTEMS CONTINUING EXPERTISE
Menlo Systems’ expertise and continuing research interests in the field of astronomy
are reflected in numerous co-authorships of its customers’ scientific publications.
The company’s technological competence is demonstrated by proprietary patents.
C O - A U T H O R S H I P I N S C I E N T I F I C P U B L I C AT I O N S
The solar gravitational redshift from HARPS-LFC Moon spectra - A test of thegeneral theory of relativity
J. I. González Hernández et al., Astronomy & Astrophysics Vol. 643, A146 (2020)
A crucial test for astronomical spectrograph calibration with frequency
combs
R. A. Probst et al., Nature Astronomy Vol. 4, p. 603 (2020)
LARS: An Absolute Reference Spectrograph for solar observations - Upgradefrom a prototype to a turn-key system
J. Löhner-Böttcher et al., Astronomy & Astrophysics Vol. 607, A12 (2017)
A compact echelle spectrograph for characterization of astro-combs
R. A. Probst et al., Appl. Phys. B 123, p. 76 (2017)
State of the Field: Extreme Precision Radial Velocities
D. A. Fischer et al., Publications of the Astronomical Society of the Pacific Vol. 128,
p. 066001 (2016)
Comb-calibrated solar spectroscopy through a multiplexed single-mode
fiber channel
R. A. Probst et al., New Journal of Physics Vol. 17, p. 023048 (2015)“High-precision calibration of highresolution spectrographs is essential
for the search for exoplanets.
The AstroComb was a significant
breakthrough in the field of astronomical
instrumentation and has revolutionized
the precision and accuracy ofspectroscopic measurements inastronomy.”
Dr. Tilo Steinmetz,
Product Manager AstroCombs

A frequency comb calibrated solar atlas
P. Molaro et al., Astronomy & Astrophysics Vol. 560, A61 (2013)
A Laser Frequency Comb System for Absolute Calibration of the VTT Echelle
Spectrograph
H.-P. Doerr et al., Solar Physics Vol. 280, p. 663 (2012)
Astronomical Spectrograph Calibration at the Exo-Earth Detection Limit
G. Lo Curto et al., ESO The Messenger Vol. 149, p. 2 (2012)
A spectrograph for exoplanet observations calibrated at the centimetre-persecond level
T. Wilken et al., Nature Vol. 485, p. 611 (2012)
Laser Frequency Combs for Astronomical Observations
T. Steinmetz et al., Science Vol. 321, p. 1335 (2008)
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TECHNOLOGY PROTECTEDB Y PAT E N T S
US6785303, US6724788, US7026594,
DE10044404, US7804863, US8995796,
US8873601, JP4668423, JP5615397,
CN103311780

AstroComb

The Most Precise Calibration Systemfor Astronomical Spectrographs
R A N G E O F S P E C I F I C AT I O N S

Output spectrum of a visible (left) and an infrared (right) AstroComb, before and after spectral flattening.

PA R A M E T E R
Optical output spectrum

C O N F I G U R AT I O N R A N G E
VIS: 450 – 1000 nm*
NIR: 1.0 – 2.3 µm*

Mode Spacing
Accuracy
Stability
Optical power per spectral line

10 - 25 GHz*3 x 10-14 in 100 s**
1 x 10-12 in 1 s**>10 nW after spectral flattening (at 18 GHz mode spacing)* others available on request** or same as reference, whichever applies firstO R D E R I N G I N F O R M AT I O N
Product CodeAstroComb

Please call for pricing. Specifications are subject to change without notice. Custom modifications are available, please inquire.

Invisible laser radiation
avoid exposure to beam
Class 4 laser

Menlo Systems GmbH
T+49 89 189 166 0
sales@menlosystems.com

www.menlosystems.com

Menlo Systems US
T+1 303 635 6406
ussales@menlosystems.com

Menlo Systems Japan
T+81 907 409 20 21jpsales@menlosystems.com

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Menlo Systems ChinaT+86 21 6071 1678
chinasales@menlosystems.com

D-AstroComb-EN 02/08/24